Late May, 1944. Churchill and Eisenhower are finishing plans for the upcoming D-Day invasion at Calais, when long-retired Sherlock Holmes is called to London by Mycroft, only to find his brother dead, clutching the shell of a barnacle in his hand. The clue leads him to a queen bee in Charles Darwin's old greenhouse in Kent. Sherlock's brilliant parsing of these clues leads him to occupied France, where a boules game reveals a secret to explosive that the D-Day landing site must be changed to avert disaster and save the last hope of stopping Hitler. But before the sixth of June, Holmes finds himself playing his most demanding role: divert a Nazi spy in the highest reaches of the Allied command, as he pursues John Watson's grandson to the scenes of his most daunting cases. The chase ends the day before the rescheduled D-Day invasion--at Baskerville Hall, where Holmes receives the shock of his life, and his most famous case is at long last resolved.